 /*******************************************************************************
  * Copyright (c) 2000, 2005 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  * Gunnar Wagenknecht - fix for bug 21756 (https://bugs.eclipse.org/bugs/show_bug.cgi?id=21756)
  *******************************************************************************/
 package org.eclipse.ui.views.properties;

 /**
  * Interface to an object which is capable of supplying properties for display
  * by the standard property sheet page implementation (<code>PropertySheetPage</code>).
  * <p>
  * This interface should be implemented by clients.
  * <code>PropertySheetPage</code> discovers the properties to display from
  * currently selected elements. Elements that implement
  * <code>IPropertySource</code> directly are included, as are elements that
  * implement <code>IAdaptable</code> and have an <code>IPropertySource</code>
  * adapter. Clients should implement this interface for any newly-defined
  * elements that are to have properties displayable by
  * <code>PropertySheetPage</code>. Note that in the latter case, the client
  * will also need to register a suitable adapter factory with the platform's
  * adapter manager (<code>Platform.getAdapterManager</code>).
  * </p>
  *
  * @see org.eclipse.core.runtime.IAdaptable
  * @see org.eclipse.core.runtime.Platform#getAdapterManager()
  * @see org.eclipse.ui.views.properties.PropertySheetPage
  * @see org.eclipse.ui.views.properties.IPropertySource2
  */
 public interface IPropertySource {

     /**
      * Returns a value for this property source that can be edited in a property
      * sheet.
      * <p>
      * This value is used when this <code>IPropertySource</code> is appearing
      * in the property sheet as the value of a property of some other
      * <code>IPropertySource</code>
      * </p>
      * <p>
      * This value is passed as the input to a cell editor opening on an
      * <code>IPropertySource</code>.
      * </p>
      * <p>
      * This value is also used when an <code>IPropertySource</code> is being
      * used as the value in a <code>setPropertyValue</code> message. The
      * reciever of the message would then typically use the editable value to
      * update the original property source or construct a new instance.
      * </p>
      * <p>
      * For example an email address which is a property source may have an
      * editable value which is a string so that it can be edited in a text cell
      * editor. The email address would also have a constructor or setter that
      * takes the edited string so that an appropriate instance can be created or
      * the original instance modified when the edited value is set.
      * </p>
      * <p>
      * This behavior is important for another reason. When the property sheet is
      * showing properties for more than one object (multiple selection), a
      * property sheet entry will display and edit a single value (typically
      * coming from the first selected object). After a property has been edited
      * in a cell editor, the same value is set as the property value for all of
      * the objects. This is fine for primitive types but otherwise all of the
      * objects end up with a reference to the same value. Thus by creating an
      * editable value and using it to update the state of the original property
      * source object, one is able to edit several property source objects at
      * once (multiple selection).
      *
      * @return a value that can be edited
      */
     public Object getEditableValue();

     /**
      * Returns the list of property descriptors for this property source. The
      * <code>getPropertyValue</code> and <code>setPropertyValue</code>
      * methods are used to read and write the actual property values by
      * specifying the property ids from these property descriptors.
      * <p>
      * Implementors should cache the descriptors as they will be asked for the
      * descriptors with any edit/update. Since descriptors provide cell editors,
      * returning the same descriptors if possible allows for efficient updating.
      * </p>
      *
      * @return the property descriptors
      */
     public IPropertyDescriptor[] getPropertyDescriptors();

     /**
      * Returns the value of the property with the given id if it has one.
      * Returns <code>null</code> if the property's value is <code>null</code>
      * value or if this source does not have the specified property.
      *
      * @see #setPropertyValue
      * @param id
      * the id of the property being set
      * @return the value of the property, or <code>null</code>
      */
     public Object getPropertyValue(Object id);

     /**
      * Returns whether the value of the property with the given id has changed
      * from its default value. Returns <code>false</code> if this source does
      * not have the specified property.
      * <p>
      * If the notion of default value is not meaningful for the specified
      * property then <code>false</code> is returned.
      * </p>
      *
      * @param id
      * the id of the property
      * @return <code>true</code> if the value of the specified property has
      * changed from its original default value, <code>false</code> if
      * the specified property does not have a meaningful default value,
      * and <code>false</code> if this source does not have the
      * specified property
      * @see IPropertySource2#isPropertyResettable(Object)
      * @see #resetPropertyValue(Object)
      */
     public boolean isPropertySet(Object id);

     /**
      * Resets the property with the given id to its default value if possible.
      * <p>
      * Does nothing if the notion of a default value is not meaningful for the
      * specified property, or if the property's value cannot be changed, or if
      * this source does not have the specified property.
      * </p>
      * <p>
      * Callers will check if this <code>IPropertySource</code> implements
      * <code>IPropertySource2</code> and this method will only be called if
      * <code>IPropertySource2#isPropertyResettable(Object)</code> returns
      * <code>true</code> for the property with the given id.
      * </p>
      *
      * @param id
      * the id of the property being reset
      * @see #isPropertySet(Object)
      * @see IPropertySource2#isPropertyResettable(Object)
      */
     public void resetPropertyValue(Object id);

     /**
      * Sets the property with the given id if possible. Does nothing if the
      * property's value cannot be changed or if this source does not have the
      * specified property.
      * <p>
      * In general, a property source should not directly reference the value
      * parameter unless it is an atomic object that can be shared, such as a
      * string.
      * </p>
      * <p>
      * An important reason for this is that several property sources with
      * compatible descriptors could be appearing in the property sheet at the
      * same time. An editor produces a single edited value which is passed as
      * the value parameter of this message to all the property sources. Thus to
      * avoid a situation where all of the property sources reference the same
      * value they should use the value parameter to create a new instance of the
      * real value for the given property.
      * </p>
      * <p>
      * There is another reason why a level of indirection is useful. The real
      * value of property may be a type that cannot be edited with a standard
      * cell editor. However instead of returning the real value in
      * <code>getPropertyValue</code>, the value could be converted to a
      * <code>String</code> which could be edited with a standard cell editor.
      * The edited value will be passed to this method which can then turn it
      * back into the real property value.
      * </p>
      * <p>
      * Another variation on returning a value other than the real property value
      * in <code>getPropertyValue</code> is to return a value which is an
      * <code>IPropertySource</code> (or for which the property sheet can
      * obtain an <code>IPropertySource</code>). In this case the value to
      * edit is obtained from the child property source using
      * <code>getEditableValue</code>. It is this editable value that will be
      * passed back via this method when it has been editted
      * </p>
      *
      * @see #getPropertyValue
      * @see #getEditableValue
      * @param id
      * the id of the property being set
      * @param value
      * the new value for the property; <code>null</code> is allowed
      */
     public void setPropertyValue(Object id, Object value);
 }

